[HEADSUP] Disallowing read() of a directory fd

[Ed Maste]

On Fri, 15 May 2020 at 13:14, Chris <bsd-lists at bsdforge.com> wrote:
>
> But given the potential
> gains for all this, are trivial at best.

Some benefits of this change have already been discussed:
1. It would have prevented, or at least significantly blunted, the
security issue described in FreeBSD-SA-19:10.ufs.
2. It avoids problems caused by application assumptions.

On the other hand, arguments for allowing reads of directories:
1. It's always been that way.
2. File system developers and experts may use the ability for certain
special or unusual actions.

Making the change with a sysctl to control still allows the special
case use, and I'm glad that Kyle spent the time on this change.